Any ideas on Metl-Span's CFR-42 SIP Roof Panel

Hi Everyone,
Let me say, first of all, I am thinking about using these panels for my house and I am not an employee or sales person for this company. In the Houston, TX area I don't think vapor migration into the roof would be much of a problem. Do you think these would work in a residential situation as kind of an instant roof without having to pay the added expense of having roofing material installed? Everybody drop me an e-mail with your thoughts.
Thanks,
John

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Todd,
Roofs like these, made out of SIP's, are usually designed to be structural as well as insulating. They are commonly used to provide the exterior as well as interior finish for the house. This is very common in timberframe installations. As such, the soffits, as well as the entire roof is sealed. Studies have shown great increases in efficiency by not having the insulation at the ceiling line but at the roof line. A vented attic space seems to cause more problems than it solves. To purposely allow moist humid air, especially in the Houston summer, and bring it in contact with cool insulation and cool floor joists, may be asking for trouble. The type of insulation, an isocyanurate, should handle the heat, especially if a lighter color was chosen for the metal exterior. With proper sealing, since the metal is bonded to the insulation, no warm air during our 1-2 month heating season should cause any condensation problems at the roofline. I know of at least two nationwide builders who are currently only building houses this way down South. The efficiency is gained by not having the air conditioning system and associated ductwork in a vented but still 135 degree attic space. With the insulation at the roofline, if the AC ductwork leaks (they all do), it leaks into air conditioned space. Unfortunately I've been up in my current attic space in the summertime here. Even with four roof vents, a ridge vent, fully vented soffit and a powered attic fan, my attic is very hot, at least 125 degrees. Venting an attic may have uses in Northern climates but has proven of little value here. I'm not saying this is the last word on the subject since I'm a novice at building design. If you have any information you could offer to refute this position I would glady like to consider it.
Thanks Todd,
John

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I am familiar with SIPs. From your first posting, I did not understand that you intended to use the Metl Span panels for anything more than just the roof sheathing and covering. Sorry about that.
I am not personally familiar with the use of the Metl Span panels in residential construction. I am, of course, familiar with standard SIPs. A few things...
1) The international Building Code calls for a minimum of 1" vented airspace beneath the roof deck. I do not know whether you're located in an area where building officials will make an issue of this.
2) I would still suggest a complete vapor barrier behind the dryall on your ceilings. (This is assuming you are planning on some sort of drywalled ceiling ... which I am not certain about.)
3) There is a difference between the larger buildings which Metl Span panels would normally be used on and a house. I would, again, strongly, urge you to spak with Metl Span and get their apporval before proceeding. Doug Pickens at Metl Span is a very nice gentleman and, if he cannot help you, he will direct you to someone who can.
Good luck.
Todd

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